1. Field of the Invention
This invention relates to a semiconductor device and a method for manufacturing the same, and more particularly to a field effect transistor (FET) having part of an active region formed in a semiconductor layer which lies in a through hole formed in a gate electrode and a method for manufacturing the same.
2. Description of the Related Art
Generally, in an FET such as a MOS (Metal-Oxide-Semiconductor) FET, MIS (Metal-Insulator-Semiconductor) FET or MES (Metal-Semiconductor) FET, active regions such as source and drain regions and channel region are formed in a semiconductor substrate. Therefore, the occupied area of the FET in the semiconductor substrate is determined by the total area of the active regions.
Most of the semiconductor integrated circuit devices such as LSIs are constructed with FETs such as MOSFETs, MISFETs or MESFETs as amplifying elements. Therefore, in order to raise the integration density of the semiconductor integrated circuit device, it is necessary to reduce the size of the FET which is a main constituent of the device.
However, the integration density required for the semiconductor integrated circuit device is getting higher. So the size of the FET for satisfying the above requirement approaches the minimum size which is needed for acting as an amplifying element. Even in this situation, it is further required for the FET to have high performance such as high-speed switching operation in order to raise up the operation speed of the integrated circuit.